U.S. patent number 4,248,810 [Application Number 05/971,320] was granted by the patent office on 1981-02-03 for foamed insulating materials and method of manufacture.
This patent grant is currently assigned to ACI Technical Centre Pty Ltd.. Invention is credited to Clive A. Erskine.
United States Patent |
4,248,810 |
Erskine |
February 3, 1981 |
Foamed insulating materials and method of manufacture
Abstract
A method of producing high temperature insulating foam is
described. A gellable foam of glass fibre, expanded perlite and
bentonite in water is shaped dried and fired at a temperature below
the temperature at which a ceramic product is formed but in excess
of the temperature at which the bentonite lattice hydroxyl water is
lost.
Inventors: |
Erskine; Clive A. (Forestville,
AU) |
Assignee: |
ACI Technical Centre Pty Ltd.
(AU)
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Family
ID: |
25518220 |
Appl.
No.: |
05/971,320 |
Filed: |
December 20, 1978 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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778666 |
Mar 17, 1977 |
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657954 |
Feb 13, 1976 |
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Current U.S.
Class: |
264/43; 264/45.3;
501/80 |
Current CPC
Class: |
C04B
33/13 (20130101); C04B 38/10 (20130101); C04B
38/10 (20130101); C04B 33/00 (20130101); C04B
38/08 (20130101) |
Current International
Class: |
C04B
38/10 (20060101); C04B 33/13 (20060101); C04B
33/02 (20060101); C04B 033/14 () |
Field of
Search: |
;264/43,45.3,DIG.49,60
;106/4R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Parrish; John A.
Attorney, Agent or Firm: Pennie & Edmonds
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of application Ser. No. 778,666
filed Mar. 17, 1977, abandoned; said application Ser. No. 778,666
is a continuation-in-part of my application Ser. No. 657,954 filed
Feb. 13, 1976, now abandoned.
Claims
I claim:
1. A method of producing a high temperature insulating foam
comprising forming with sufficient water to produce a gellable
foam, a mixture of components in the following proportions,
expressed as percentages by weight of the components of the total
composition, excluding water:
foaming the mixture, shaping the foamed mixture, drying the shaped
foam and firing the dried foam at a temperature lower than
900.degree. C. and in excess of the temperature at which the
bentonite lattice hydroxyl water is lost, said temperature being
below the temperature at which a ceramic product is formed.
2. A method according to claim 1, wherein the components of the
composition are present in the following weight proportions:
3. A method according to claim 1, wherein the glass fibre is E
glass fibre.
4. A method according to claim 1, wherein the firing temperature
lies within the range of 650.degree. C. to 850.degree. C.
5. A method according to claim 4, wherein the firing temperature
lies within the range 680.degree. C. to 720.degree. C.
6. A method according to claim 3, wherein the firing temperature is
lower than the softening point of E glass fibre.
7. A method according to claim 1, wherein the composition includes
a surfactant.
8. A method according to claim 7, wherein the surfactant does not
exceed 2% by weight of the total composition, including water.
9. A method according to claim 1, wherein the composition is foamed
by mechanical entrainment of air.
10. A method according to claim 1, wherein the dried foam is fired
for a time sufficiently long as to allow all parts of the dried
foam to be at the firing temperature for at least two hours.
11. A method according to claim 1, wherein the insulating foam has
a density within the range 95 to 500 kg/m.sup.3.
12. A method according to claim 1, wherein the insulating foam has
a modulus of rupture falling within the range 150 to 1,000 kPa.
13. A method according to claim 1, wherein the insulating foam has
a thermal conductivity in the range 0.1 to 0.2 w/m.K at 500.degree.
C.
Description
This invention relates to methods for the production of high
temperature insulating materials and products produced thereby.
High temperature insulating materials are used in areas where
operating hot face temperatures are greater than 350.degree. C. and
normally less than 1000.degree. C. Materials used within this range
include calcium silicate, felted textile glass fibre, mineral fibre
and ceramic fibre. Calcium silicate has a particular advantage
where a rigid, self-supporting material is required, while the
fibrous types are preferred where flexibility is required.
Normally, no single material effectively covers the whole high
temperature range, either because of economic considerations or
because of degradation above a particular limiting temperature.
Applicants have sought to provide an insulating material which is
complementary to the above range of materials and which can be used
as an alternative to such materials where reasons such as
difficulties in manufacture and supply or specific unsatisfactory
physical properties of the materials concerned leave an opening for
an alternative.
In this regard applicants have found that an insulating material
can be manufactured from formulations comprising mixtures of
expanded perlite and bentonite.
The expanded perlite used in the compositions is derived from a
perlite rock, a volcanic glass found in association with acid
igneous lavas such as rhyolite. Generally speaking, it is compact,
non-crystalline, grey-black or red in colour and normally contains
up to 5% water of composition. The rock usually has a vitreous to
waxy lustre and its structure ranges from massive to a friable
composite of columnar needles. Concentric banding is common.
Hardness on the Mohs scale is between 5.5 and 7 and the bulk
density of crude perlite is in the region of 2250 kg/m.sup.3.
When crushed and heated rapidly to temperatures in the range
750.degree.-1200.degree. C., the material expands to form expanded
perlite, a material consisting of cellular masses with up to twenty
times the volume of the original material.
The preferred perlite work material for the manufacture of
insulation according to the invention is ore containing 3-4% water
of composition crushed to pass 36 mesh BSS and expanded at a
maximum temperature of 1000.degree.-1200.degree. C. The expanded
material should preferably have a bulk density of 30-60
kg/m.sup.3.
Bentonite is a montmorillonite-type clay with sodium as the
principal exchangeable cation.
Chemically, montmorillonite is described as a hydrous aluminium
silicate containing small amounts of alkali and alaline earth
metals. Structurally, montmorillonite consists of two basic
building blocks; the aluminium octahedral sheet and the silica
tetrahedral sheet. A single montmorillonite unit cell consists of
two silica tetrahedral sheets, between which is an aluminium
octahedral sheet. The negative charge of the montmorillonite
lattice is balanced by cations which can be readily exchanged. In
naturally occurring montmorillonites, the exchangeable cations are
usually sodium and calcium.
Bentonites have the property of forming thixotropic gels with water
by adsorption on the basal surfaces with a corresponding increase
in the c-axis dimension. This adsorbed water is lost on heating to
100.degree.-200.degree. C. but hydroxyl lattice water usually
remains until the clay is heated to 700.degree.-800.degree. C.,
although some of the less well known forms of bentonite can lose
lattice hydroxyl at temperatures in the region of 600.degree. C.
When the hydroxyl water is lost, bentonite will no longer adsorb
water on the basal surfaces and loses its property to disperse in
water.
Applicants have found that foamed insulating materials based on
perlite-bentonite can often be used as an alternative to calcium
silicate insulation. Moreover, the process components required for
manufacturing the material can consist of entirely simple
conventional equipment. A foam of the components can be produced
chemically or mechanically without the use of high speed mixing
equipment and the foamed slurry is simply shaped by conventional
casting or pressing techniques, dried and fired. This compares
favourably with processes for manufacturing calcium silicate which
requires large capital outlays to cover the costs of steam
generators and autoclaves.
Furthermore, unlike calcium silicates, applicant's material is not
in a hydrated form and does not suffer degradation of required
properties at operating temperatures. As a result, advantages of
applicant's material over calcium silicate often include
comparatively lower shrinkage and reduced liberation of dust during
use. Applicant's process also has the advantage that it produces a
"foamed foam" compared with a simple one stage foam produced by
alternative techniques. The perlite used in the composition is
itself expanded or foamed prior to incorporation and the
composition is then foamed further to produce a mouldable gel
having a "foamed foam" structure. There are obvious weight and
insulating advantages to be gained once it is possible to produce
such a "foamed foam" structure.
The products of the invention differ markedly from the conventional
lightweight clay based materials such as those described in U.S.
Pat. No. 3,689,611 which rely on the use of a foamed or expanded
aggregate to give lightweight properties, but do not have a "foamed
foam" structure. Such materials are generally formed by firing at
high temperatures to give a ceramic bond. Thus the properties of
the finished material differ markedly from the products of the
invention which are characterised by a relatively low temperature
firing which does not result in the formation of ceramic articles,
but causes dehydroxylation of the clay, thereby preventing
redispersion in water.
Applicant's process is made possible because of the unexpected
properties of the foam during the drying step prior to firing.
Generally, foams of this sort collapse on drying unless they
include a setting agent or set of themselves, as does aerated
concrete. Furthermore, the introduction of setting agents in many
compositions can lead to undesirable operating properties such as
unacceptable temperature expansion which leads to cracking. Unlike
other foams, the foam of perlite and bentonite does not collapse
during drying, even though it is not set and does not include a
setting agent. As a result, the manufacturing process for
applicant's insulating material is unexpectedly simple and
inexpensive.
The invention provides a method of producing a high temperature
insulating foam comprising forming with sufficient water to produce
a gellable foam, a mixture of components in the following
proportions expressed as percentages by weight of the components of
the total composition, excluding water:
______________________________________ Glass fibre 1/2 to 20%
Expanded perlite 40% to 95% Bentonite 5% to 40%
______________________________________
foaming the mixture, shaping the foamed mixture, drying the shaped
foam and firing the dried foam at a temperature in excess of the
temperature at which the bentonite lattice hydroxyl water is lost,
but below 900.degree. C., and preferably in the range 650.degree.
C. to 850.degree. C.
In a preferred form of the invention the components of the mixture
are present in the following proportions:
______________________________________ Glass fibre 1% to 5%
Expanded perlite 70% to 85% Bentonite 10% to 30%
______________________________________
The preferred glass fibre material is E glass fibre which, in the
form of a lightly sized roving with a filament diameter of about 12
microns, chopped to lengths of 10-50 mm, has been found to be
satisfactory for the process. The type of size does not appear to
greatly affect either the mixing process or the product. Unsized
fibre is also satisfactory.
As a major purpose of the glass fibre is to give the shaped foamed
composition "green" strength prior to firing, the presence of glass
fibre is in some cases not required thereafter, and in such cases
it is possible to fire at temperatures above the softening point of
the glass fibre. However, if the foam is destined for use where a
high degree of flexural strength is required, the firing conditions
for the foam may be modified to ensure that the firing temperature
never exceeds the softening temperature of the glass fibre which is
slightly above 700.degree. C. In this way, it is possible to
produce a fibre reinforced final product with all the physical
advantages fibre reinforcement generally entails.
Surfactant preferably in quantities not exceeding 2% by weight of
the total composition may also be included to improve foaming. The
choice of surfactant used for the composition, if any, is not
critical as practically any material or mixture of materials having
the capacity of lowering the surface tension of water can be used.
Examples of suitable surfactants are listed below:
Octa-decylamine ethoxylate
Alcohol ethoxylate
Nonyl-phenol ethoxylate
Coconut oil alkylolamide
Sodium fatty alcohol ethoxylate sulphate
Sodium nonyl-phenol ethoxylate sulphate
Sodium alkyl-ether sulphate
Sodium dodecyl-benzene sulphate
Sodium alkylnaphthalene sulphate
Sodium lauryl sulphate
The invention will now be described in more detail with reference
to the following three examples of formulations suitable for
performance of the invention.
EXAMPLE I
The perlite required for this formulation is produced from -36 mesh
BSS perlite ore expanded to give a product with a bulk density of
30-60 kg/m.sup.3.
The bentonite required has sodium as its major replaceable cation.
A bentonite found suitable for use has the following chemical
composition.
______________________________________ SiO.sub.2 69.3% Al.sub.2
O.sub.3 12.2% Fe.sub.2 O.sub.3 3.1% TiO.sub.2 0.26% K.sub.2 O 0.42%
Na.sub.2 O 3.1% MgO 2.7% CaO 2.6% Loss on Ignition (1000.degree.
C.) 6.07% ______________________________________
Glass fibre used successfully in the laboratory preparation of the
formulation is 60 end continuous roving K filament E-glass, chopped
to 13 mm lengths. In large-scale batch preparation, the fibre
length can be increased.
The surfactant used in this formulation is nonylphenol ethoxylate.
The formulation is:
______________________________________ Water 66.67% by weight
Perlite 26.67% by weight Bentonite 5.97% by weight Glass fibre
0.67% by weight Surfactant 0.02% by weight
______________________________________
EXAMPLE II
The high degree of variability in the characteristics of
bentonites, and the range of particle sizes that can be produced by
expanding perlite ore, require variation in the formulation to
ensure a satisfactory product.
Wyoming (US) bentonites have a high capacity for adsorbing water
but require a higher level of surfactant than some other bentonites
to produce a material of the same density. By adjustment of the
perlite, bentonite and surfactant levels, a product of similar
properties can be produced:
______________________________________ Water 66.67% by weight
Perlite 29.26% by weight Wyoming Bentonite 3.32% by weight Glass
fibre 0.67% by weight Surfactant 0.08% by weight
______________________________________
In this case the perlite, glass fibre and surfactant described in
Example I are retained. The bentonite has the following chemical
composition:
______________________________________ SiO.sub.2 62.0% Al.sub.2
O.sub.3 20.9% Fe.sub.2 O.sub.3 3.8% TiO.sub.2 0.15% K.sub.2 O 0.47%
Na.sub.2 O 2.2% MgO 2.7% CaO 1.2% Loss of Ignition (1000.degree.
C.) 5.60% ______________________________________
It is also possible to use combinations of bentonites in the
formulation.
Variations in perlite grade can be accommodated in the formulation
by similar adjustments to the bentonite/perlite ratio and
surfactant level. Generally, perlite coarser than the preferred
size requires a lower bentonite/perlite ratio, perlite finer than
the preferred size requires a higher bentonite/perlite ratio.
Density control is achieved by variations in the surfactant level,
provided the formulation and mixing process are held constant.
In a production situation, waste generated by the trimming of
products can be crushed to pass 10 mesh BSS and used to partially
replace the perlite component of the mix.
EXAMPLE III
In some applications, a relatively thin insulating board is
required. Asbestos millboard is no longer used in many such
applications because of the asbestos dust hazard. A modification to
the formulation can be made to provide a suitable alternative to
asbestos millboard. Using the preferred materials for Example I, an
insulating board can be made using the following proportions of
materials:
______________________________________ Water 66.67% by weight
Perlite 25.00% by weight Bentonite 6.65% by weight Glass fibre
1.67% by weight Surfactant 0.01% by weight
______________________________________
The strength of the product can be increased by an increase in
either the fibre level or fibre length used. In both cases there is
some loss in casting properties.
The processing of the compositions disclosed in Examples I to III
is carried out in five major steps:
______________________________________ Step
______________________________________ WEIGHING 1 MIXING 2 CASTING
OR PRESSING 3 DRYING 4 FIRING 5
______________________________________
1. Weighing
The quantities of materials required for the batch are weighed and
held separately. The perlite is weighed as two separate equal
portions.
2. Mixing
Mixers suitable for the process include sigma blade, planetary,
ribbon and paddle types. The planetary type mixer is preferred.
(a) Water and surfactant are placed in the mixer and mixing is
commenced;
(b) Bentonite is added and the mixing is continued until the clay
is dispersed;
(c) About half of the perlite is added and mixing is continued
until a foamed slurry is produced;
(d) Glass fibre is added while mixing;
(e) The remaining perlite is added and mixing is continued until a
foamed slurry is again produced.
As a variation to (a) the bentonite, water and surfactant may be
pre-mixed and held until required. This procedure has the advantage
of allowing the bentonite a longer time for water adsorption, and
leads to better dispersion of binder in the product.
3. Casting or Pressing
Because of the high water level of the slurry, it is preferable to
cast in porous moulds to provide a maximum surface area for drying.
For block insulation, corrugated board boxes have been found to
provide sufficient support for the wet slurry. Pipe sections and
other shapes can be encased in suitably shaped moulds, or
alternatively, machined from the block insulation product.
The slurry can be gravity fed into moulds, using a small degree of
vibration to ensure the filling of corners and to avoid the
entrainment of large air bubbles. Alternatively, the slurry can be
injected into moulds under pressure. For thin sections such as
boards up to 50 mm thick, metal trays can be used as moulds if
de-moulding is carried out before the firing stage.
For casting, the slurry should have a consistency similar to
whipped cream. Adjustments to the solids/water ratio can be made to
achieve the correct casting properties--this is best done by a
trial and observation technique.
As a variation of (e) mixing may be terminated anytime after the
second portion of expanded perlite has been adequately dispersed.
This procedure can provide a mix of suitable consistency for
shaping by a conventional pressing process, thus avoiding the large
mould inventory required if a casting process is used. By
adjustment of the mixing time, the consistency of the final mix can
be varied to suit the particular moulding conditions employed.
If the variation to part (e) of the mixing procedure is used, it is
possible to press some shapes, such as rectangular blocks, which
will retain their pressed dimensions after demoulding, provided
they are supported on their lower surface by an inflexible
material. Generally, a pressing load of 100-500 kPa is
sufficient--higher loads lead to the formation of pressing
laminations.
A pressing process found suitable for use in the production of
rectangular blocks is:
(a) a mould, with a removable base of rigid flat sheet material, is
charged with the mixture;
(b) a load is applied evenly over the upper surface for a period of
about 5 seconds;
(c) the material and support sheet are ejected from the mould.
4. Drying
Drying is commenced at 80.degree. C. or less, and the temperature
is then gradually raised as a hard shell forms at the surface of
the shape. The drying stage may continue without interruption to
the firing stage, through a progressive increase in temperature, or
it may be terminated when the material is essentially dry and can
be transferred without damage to a furnace.
Drying times depend on the volume and geometry of the shape. As a
guide, a block 300 mm.times.300 mm.times.300 mm can be considered
dry after 72 hours at a continuous temperature of 80.degree. C. in
a corrugated board mould. Any remaining water is released during
the firing stage.
The rate of temperature increase during the drying process and the
terminal temperature are dependent upon the volume of the shape and
the drying equipment being used. The material does not have a high
drying sensitivity, but surface cracks can form if the slurry is
not supported sufficiently well in the mould, and the expansion of
entrained air produces a volume increase. This is particularly
evident if the upper surface is not restrained during the early
stages of the drying process.
Linear drying shrinkage is normally less than 0.1%, measured on a
sample dimension of 300 mm.
5. Firing
The firing temperature must exceed the temperature at which the
bentonite lattice hydroxyl water is lost, but preferably must not
exceed the temperature at which the reinforcing fibre suffers
excessive degradation. In general, the operating temperature range
is 680.degree.-720.degree. C.
The shapes are fired for a sufficient time for the centre of the
thickest portion to be at the firing temperature for two hours. If
the material is completely dry before firing, it can be placed
directly in a furnace operating at the firing temperature.
Similarly, after the required firing time has elapsed, the material
may be removed from the furnace to cool in an ambient temperature
atmosphere without thermal shock damage.
If the product is required for an application in which the
reinforcing properties of the fibre are not required, the firing
temperature can be increased beyond the recommended temperature to
850.degree. C. to 870.degree. C. At these temperatures, a higher
compressive strength is developed, but the material becomes more
brittle.
Linear firing shrinkage within the recommended temperature range is
less than 0.2%, measured on a sample dimension of 300 mm.
PROCESS FLOW CHART
Flow sheet 1 shows the process in its simplest form (FIG. 1). Raw
materials are numbered to indicate the order of introduction to the
mixing vessel.
An alternative flow sheet 2 is shown hereunder. This is essentially
the same as the previous flow sheet, but includes the refinements
of a separate mixing process for the clay, and a holding tank to
permit a continuous casting process.
PHYSICAL PROPERTIES
The physical properties of the product vary according to the type
of raw materials used, the formulation and process variables.
However, for material produced from the formulation of Example 1,
the following properties have been measured:
______________________________________ Density 225 kg/m.sup.3
Modulus of rupture 320 kPa Compressive Strength 280 kPa Thermal
Conductivity 0.13 w/m.K at 500.degree. C.
______________________________________
With suitable variations to the formulation, a material can be
produced within a density range of 95-500 kg/m.sup.3. Generally,
modulus of rupture, compressive strength and thermal conductivity
each increase as the density increases, the preferred values for
these properties falling within the ranges 150 to 1,000 kPa; 150 to
1,000 kPa and 0.1 to 0.2 w/m.K at 500.degree. C., respectively.
Unlike calcium silicate, the product has a very low in-service
shrinkage. Dimensional changes at temperatures up to 800.degree. C.
are almost negligible. At 900.degree. C. however, shrinkage is
considerable, and a realistic maximum service temperature for the
product is about 850.degree. C.
Whilst the foregoing Examples deal exclusively with the production
of a foam by mechanical mixing, it is equally possible to use
conventional chemical foamants to cause foaming and the manner of
use of such foamants would be well within the purview of the person
skilled in this art.
* * * * *